Already known in the art are catalytic converter systems for internal combustion engines for motor vehicles, by which pollutants in the exhaust gases of internal combustion engines can be converted into harmless or less harmful components. Such catalytic converter systems typically comprise a catalytic converter often arranged close to the engine and comprising a catalytically effective noble metal depletion of the platinum group, particularly consisting of the elements platinum, palladium and rhodium. Since platinum has a low temperature stability, noble metal depletions comprising the elements palladium and rhodium are preferred, wherein rhodium is applied due to its reducing effect on the nitrogen oxide (NOx) conversion and palladium is applied due to its oxidizing effect on the carbon hydride (HC) and carbon monoxide (CO) conversions.
The noble metal depletion of the catalytic converters exhibits a considerable cost factor, however, may not be reduced arbitrarily, if the legal exhaust gas standards for internal combustion engines and motor vehicles, respectively, shall be fulfilled. Particularly, a weight ratio of 5:1 of the elements palladium and rhodium and a specific depletion comprising rhodium of 6.66 g/ft3 in relation to the catalytic converter volume VK is currently required in the noble metal depletion in order to obtain the European Exhaust Gas Standard EU 4. The values mentioned for the specific depletion comprising rhodium correspond to a absolute depletion comprising rhodium of 0.0296 g for a catalytic converter having a volume of 1.258 liters and to a absolute depletion of 0.0236 g for a catalytic converter having a volume of 1 liter, wherein in each case a cell density of 600 cpsi (cells per square inch) and a wall thickness of the passages passed by the exhaust gas of 4.3 mil (1 mil=0.0254 mm) was assumed. Since the price per gram of rhodium is higher by about a factor 10 than the price per gram of palladium, it is clear, that a reduction of the relative and absolute rhodium depletion of a catalytic exhaust gas converter is desirable because of cost reasons as well as for a sustainable resource management.
A main factor so far opposing a reduction of the rhodium depletion was, that the exhaust gas converter specific startup or light off temperature following a cold start when using a reduced rhodium depletion of the catalytic converter could not be reached fast enough in order to fulfill the legal exhaust gas emission limit values at least when operating according to the New European Driving Cycle.